The CONSORT Statement: Revised Recommendations for Improving the Quality of Reports of Parallel-Group Randomized Trials

To comprehend the results of a randomized controlled trial (RCT), readers must understand its design, conduct, analysis, and interpretation. That goal can be achieved only through complete transparency from authors. Despite several decades of educational efforts, the reporting of RCTs needs improvement. Investigators and editors developed the original CONSORT (Consolidated Standards of Reporting Trials) statement to help authors improve reporting by using a checklist and flow diagram. The revised CONSORT statement presented in this article incorporates new evidence and addresses some criticisms of the original statement.

The checklist items pertain to the content of the Title, Abstract, Introduction, Methods, Results, and Comment. The revised checklist includes 22 items selected because empirical evidence indicates that not reporting the information is associated with biased estimates of treatment effect or because the information is essential to judge the reliability or relevance of the findings. We intended the flow diagram to depict the passage of participants through an RCT. The revised flow diagram depicts information from 4 stages of a trial (enrollment, intervention allocation, follow-up, and analysis). The diagram explicitly includes the number of participants, according to each intervention group, included in the primary data analysis. Inclusion of these numbers allows the reader to judge whether the authors have performed an intention-to-treat analysis.

In sum, the CONSORT statement is intended to improve the reporting of an RCT, enabling readers to understand a trial's conduct and to assess the validity of its results.

A report of a randomized controlled trial (RCT) should convey to the reader, in a transparent manner, why the study was undertaken and how it was conducted and analyzed. For example, a lack of adequately reported randomization has been associated with bias in estimating the effectiveness of interventions.^1,2 To assess the strengths and limitations of an RCT, readers need and deserve to know the quality of its methods. Despite several decades of educational efforts, RCTs still are not being reported adequately.^3-6 For example, a review of 122 recently published RCTs that evaluated the effectiveness of selective serotonin reuptake inhibitors as first-line management strategy for depression found that only 1 (0.8%) article described randomization adequately.⁵ Inadequate reporting makes the interpretation of RCT results difficult if not impossible. Moreover, inadequate reporting borders on unethical practice when biased results receive false credibility.

In the mid 1990s, 2 independent initiatives to improve the quality of reports of RCTs led to the publication of the CONSORT (Consolidated Standards of Reporting Trials) statement,⁷ which was developed by an international group of clinical trialists, statisticians, epidemiologists, and biomedical editors. CONSORT has been supported by a growing number of medical and health care journals^8-11 and editorial groups, including the International Committee of Medical Journal Editors¹² (ICMJE, also known as the Vancouver Group), the Council of Science Editors (CSE), and the World Association of Medical Editors (WAME). CONSORT is also published in Dutch, English, French, German, Japanese, and Spanish. It can be accessed on the Internet, along with other information about the CONSORT group.¹³

The CONSORT statement comprises a checklist and flow diagram for reporting an RCT. For convenience, the checklist and diagram together are called simply CONSORT. They are primarily intended for use in writing, reviewing, or evaluating reports of simple 2-group parallel RCTs.

Preliminary data indicate that the use of CONSORT does indeed help to improve the quality of reports of RCTs.^14,15 In an evaluation of 71 published RCTs in 3 journals in 1994, allocation concealment was reported unclearly in 43 (61%) of the trials.¹⁴ Four years later, after these 3 journals required that authors reporting an RCT use CONSORT, the proportion of articles in which allocation concealment was reported unclearly had decreased to 30 of 77 (39%; mean difference, −22%; [95% confidence interval, −38% to −6%]).¹⁴

The usefulness of CONSORT is enhanced by continuous monitoring of the biomedical literature; this monitoring allows CONSORT to be modified depending on the merits of maintaining or dropping current items and including new items. For example, when Meinert¹⁶ observed that the flow diagram did not provide important information about the number of participants who entered each phase of an RCT (enrollment, treatment allocation, follow-up, and data analysis), the diagram was able to be modified to accommodate the information. The checklist is similarly flexible.

This iterative process makes the CONSORT statement a continually evolving instrument. While participants in the CONSORT group and their degree of involvement vary over time, members meet regularly to review the need to refine CONSORT. At the 1999 meeting, participants decided to revise the original statement. This report reflects changes determined by consensus of the CONSORT group, partly in response to emerging evidence on the importance of various elements of RCTs.

Thirteen members of the CONSORT group met in May 1999 with the primary objective of revising the original CONSORT checklist and flow diagram, as needed. The group discussed the merits of including each item in the light of current evidence. As in developing the original CONSORT statement, our intention was to keep only those items deemed fundamental to reporting standards for an RCT. Some items not considered essential may well be highly desirable and still should be included in an RCT report even though they are not included in CONSORT. Such items include approval of an institutional ethical review board, sources of funding for the trial, and a trial registry number (eg, the International Standard Randomized Controlled Trial Number [ISRCTN]) used to register the RCT at its inception.¹⁷

Shortly after the meeting, a revised version of the checklist was circulated to the group for additional comments and feedback. Revisions to the flow diagram were similarly made. All these changes were discussed when CONSORT participants met in May 2000, and the revised statement was finalized shortly afterward.

The revised CONSORT statement includes a 22-item checklist (Table 1) and a flow diagram (Figure 1). Its primary aim is to help authors improve the quality of reports of simple 2-group parallel RCTs. However, the basic philosophy underlying the development of the statement can be applied to any design. In this regard, additional statements for other designs will be forthcoming from the group.¹³ CONSORT can also be used by peer reviewers and editors to identify reports with inadequate description of trials and those with potentially biased results.^1,2

During the 1999 meeting, the group also discussed the benefits of developing an explanatory document to enhance the use and dissemination of CONSORT. The document is patterned on reporting of statistical aspects of clinical research¹⁸ and was developed to help facilitate the recommendations of the ICMJE's Uniform Requirements for Manuscripts Submitted to Biomedical Journals. Three members of the CONSORT group, with assistance from members on some checklist items, drafted an explanation and elaboration document. That document¹⁹ was circulated to the group for additions and revisions and was last revised after review at the latest CONSORT group meeting.

(1) In the revised checklist, a new column for "paper section and topic" integrates information from the "subheading" column that was contained in the original statement.

(2) The "Was it reported?" column has been integrated into a "reported on page #" column, as requested by some journals.

(3) Each item of the checklist is now numbered and the syntax and order have been revised to improve the flow of information.

(4) "Title" and "Abstract" are now combined in the first item.

(5) While the content of the revised checklist is similar to the original, some items that previously were combined are now separate. For example, authors had been asked to describe "primary and secondary outcome(s) measure(s) and the minimum important difference(s), and indicate how the target sample size was projected." In the new version, issues pertaining to outcomes (item 6) and sample size (item 7) are separate, enabling authors to be more explicit about each. Moreover, some items request additional information. For example, for outcomes (item 6) authors are asked to report any methods used to enhance the quality of measurements, such as multiple observations.

(6) The item asking for the unit of randomization (eg, cluster) has been dropped because specific checklists have been developed for reporting cluster RCTs²⁰ and other design types¹³ since publication of the original checklist.

(7) Whenever possible, new evidence is incorporated into the revised checklist. For example, authors are asked to be explicit about whether the analysis reported is by intention-to-treat (item 16). This request is based in part on the observations²¹ that authors do not adequately describe and apply intention-to-treat analysis and reports that not providing this information are less likely to provide other relevant information, such as loss to follow-up.²²

(8) The revised flow diagram depicts information from 4 stages of a trial (enrollment, intervention allocation, follow-up, and analysis). The revised diagram explicitly includes the number of participants, according to each intervention group, included in the primary data analysis. Inclusion of these numbers lets the reader know whether the authors have performed an intention-to-treat analysis,.^21-23 Because some of the information may not always be known and to accommodate other information, the structure of the flow diagram may need to be modified for a particular trial. Inclusion of the participant flow diagram in the report is strongly recommended but may be unnecessary for simple trials, such as those without any participant withdrawals or dropouts.

Specifically developed to guide authors about how to improve the quality of reporting of simple 2-group parallel RCTs, CONSORT encourages transparency in reporting the methods and results so that reports of RCTs can be interpreted both readily and accurately. However, CONSORT does not address other facets of reporting that also require attention, such as scientific content and readability of RCT reports. Some authors, in their enthusiasm to use CONSORT, have modified the checklist.²⁴ We recommend against such modifications because they may be based on a different process than the one used by the CONSORT group.

The use of CONSORT seems to reduce (if not eliminate) inadequate reporting of RCTs.^14,15 Potentially, the use of CONSORT should positively influence the manner in which RCTs are conducted. Granting agencies have noted this potential relationship and, in at least 1 case,²⁵ have encouraged grantees to consider in their application how they have dealt with the CONSORT items.

The evidence-based approach used to develop CONSORT also has been used to develop standards for reporting meta-analyses of randomized trials,²⁶ meta-analyses of observational studies,²⁷ and diagnostic studies (Jeroen Lijmer, MD, written communication, October 2000). Health economists also have started to develop reporting standards²⁸ to help improve the quality of their reports.²⁹ The intent of all these initiatives is to improve the quality of reporting of biomedical research³⁰ and by doing so to bring about more effective health care.

The revised CONSORT statement will replace the original one in the journals and groups that already support it. Journals that do not yet support CONSORT may do so by registering on the CONSORT Web site.¹³ To convey to authors the importance of improved quality in the reporting of RCTs, we encourage supporting journals to reference the revised CONSORT statement and the CONSORT Internet address¹³ in their "Instructions to Authors." Because the journals publishing the revised CONSORT statement have waived copyright protection, CONSORT is now widely accessible to the biomedical community. The CONSORT checklist and flow diagram can also be accessed at the CONSORT Web site.¹³

A lack of clarification of the meaning and rationale for each checklist item in the original CONSORT statement has been remedied with the development of the CONSORT explanation and elaboration document,¹⁹ which also can be found on the CONSORT Web site.¹³ This document reports the evidence on which the checklist items are based, including the references, which had annotated the checklist items in the previous version. We encourage journals to also include reference to this document in their Instructions to Authors.

Emphasizing the evolving nature of CONSORT, the CONSORT group invites readers to comment on the updated checklist and flow diagram through the CONSORT Web site.¹³ Comments and suggestions will be collated and considered at the next meeting of the group in 2001.